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Anaesthetic FRCA Primary - eLFH Obstetrics > eLFH - Physiological changes during Pregnancy > Flashcards

eLFH - Physiological changes during Pregnancy Flashcards

1
Q

Usual weight gain during pregnancy

A

10 to 20 kg

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2
Q

Recommended weight gain for women with normal pre-pregnancy BMI

A

11.5 to 16 kg

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3
Q

Cause of weight gain during pregnancy

A

Foetal growth
Placenta
Amniotic fluid
Uterus
Breasts
Fat
Blood
Extravascular extracellular fluid

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4
Q

Cause of aortocaval compression

A

Weight of gravid uterus compress great vessels against lumbar vertebral bodies

(IVC > Aorta)

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5
Q

Consequence of aortocaval compression

A

IVC obstruction causes fall in venous return to heart leading to drop in maternal cardiac output and BP

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6
Q

Common alternative name for aortocaval compression

A

Supine hypotension

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7
Q

Symptoms of aortocaval compression

A

Dizzy
Nausea

Therefore women usually learn to avoid this position

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8
Q

Consequence if aortic compression predominates aortocaval compression

A

Maternal BP (measured above level of compression) will be normal or raised

However blood supply to uterus and fetoplacental unit (originates below level of compression) reduces and compromises foetus without maternal hypotension

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9
Q

Azygous venous system

A

Internal vertebral venous plexus around spinal cord

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10
Q

Consequence of IVC compression on azygous venous system

A

Azygous venous system becomes dilated with IVC compression

Causes engorgement of veins within the spinal canal

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11
Q

Degree of tilt to left side required to reliably avoid aortocaval compression

A

15 degrees

Full left lateral position impractical for obstetric procedures

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12
Q

Gestation from which left lateral tilt is required

A

20 weeks onwards

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13
Q

Approximate uterine blood flow at term

A

700 ml/min

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14
Q

Blood supply to the uterus

A
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15
Q

Graph of changes to heart rate, stroke volume and cardiac output during pregnancy with weeks gestation

A
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16
Q

Why does cardiac output increase further during labour and by how much

A

CO increases by further 40% due to pain

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17
Q

Why does cardiac output increase immediately following delivery

A

Autotransfusion of blood from the uterus

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18
Q

Average resting heart rate during pregnancy

A

85 bpm

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19
Q

Changes to blood pressure during pregnancy

A

Systolic and diastolic pressure fall (diastolic more so than systolic) and then increases back to pre-pregnancy BP by term

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20
Q

Gestation at which BP is at its lowest

A

20 weeks

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21
Q

Cause for drop in BP during pregnancy

A

Fall in systemic vascular resistance

MAP = CO x SVR

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22
Q

Spirometry trace of non-pregnant vs pregnant adult

A
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23
Q

Lung volumes which are increased in pregnancy

A

Tidal volume
Respiratory rate
Minute ventilation

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24
Q

Lung volumes which are reduced in pregnancy

A

Functional residual capacity
Expiratory reserve volume
Residual volume
Total lung capacity

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25
Q

Why does pregnancy cause faster fall i PaO2 during apnoea

A

Reduced FRC
Higher oxygen demands

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26
Q

Recommended pre-oxygenation method for pregnancy GA

A

3 minutes tidal breathing

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27
Q

Why does end tidal oxygen concentration rise faster in pregnant women

A

Higher minute ventilation in pregnancy

28
Q

When does PaCO2 decrease during pregnancy and implication

A

Early in pregnancy
Often lower PaCO2 present in women anaesthetised for termination of pregnancy or ectopic pregnancy

29
Q

Changes to ventilator settings for term LSCS under GA

A

Slightly higher RR and VT
Targeting lower EtCO2 / PaCO2 of 4.1

30
Q

Alveolar gas equation

A
31
Q

Why does PaO2 rise as PaCO2 falls during pregnancy

A

Alveolar partial pressure O2 increases as per alveolar gas equation

Therefore higher diffusion gradient into arterial blood

32
Q

Cause for more difficult intubation in pregnancy

A

Mucosa more vascular and oedematous
Subtly alters laryngoscopy views

33
Q

Reason to avoid nasal intubation, NG tube or suction to nose during pregnancy

A

Increased vascularity of mucosa increases chance of haemorrhage

34
Q

Changes to contents of chest during pregnancy

A

Diaphragm and chest contents displaced cephalad as pregnancy advances

AP diameter of chest increases to accommodate this

35
Q

Changes to carina during pregnancy

A

Carina displaced cephalad as pregnancy advances
Therefore shorter distance from teeth to carina and higher chance of endobronchial intubation

36
Q

Changes to heart during pregnancy

A

Heart is enlarged and pulmonary vessel engorgement

37
Q

ECG changes during pregnancy

A

Left axis shift
T wave inversion in V2

38
Q

GI changes during pregnancy

A

Gastro-oesophageal reflux

39
Q

Reasons for increased gastro-oesophageal reflux during pregnancy

A

Lower oesophageal sphincter tone reduced

After 20 weeks reflux promoted by gravid uterus

Increased gastric contents volume

40
Q

Changes to gastric contents during pregnancy

A

pH falls (3.0 -> 2.4)

Volume increases (0.24 -> 0.49 ml/kg)

41
Q

Risks of GA which are increased in pregnancy

A

Gastric contents aspiration

Hypoxaemia

Death

(Due to GI changes and reduced time for airway manipulation)

42
Q

Methods to reduce risks from GI changes

A

Reduce gastric acidity

RSI

43
Q

Gestation from which all pregnant women should have RSI and considered high risk of aspiration

A

All women over 16 - 18 weeks should have RSI

Prior to 16 weeks gestation, if there are no other risk factors, then RSI is not mandatory

44
Q

How soon after delivery is RSI still mandatory for GA

A

Withing 48 hours of delivery RSI is mandatory

After 48 hours, risk of gastric contents returns to pre-pregnancy levels

45
Q

Haematological changes in pregnancy

A

Plasma volume rises
RBC volume increases
Hypercoagulability

46
Q

Why does Hb concentration fall during pregnancy

A

RBC volume increase to compensate for blood loss at delivery, but not as much as plasma volume increases, therefore [Hb] falls

47
Q

Lower limit of normal Hb concentration for pregnant women

A

110

48
Q

Cause of hypercoagulability in pregnancy and therefore raised VTE risk

A

Raised plasma levels of:
- Fibrinogen
- Factor VII
- Factor X
- Factor XII

Decreased fibrinolysis

49
Q

Neurological changes in pregnancy with implication on anaesthesia

A

Reduced doses of drugs are required to induce and maintain general and regional anaesthesia

MAC for inhaled agents typically reduced by ~30%

From late first trimester onwards local anaesthetic dose typically reduced by ~30% for regional anaesthesia

Induction dose for IV agents also reduced

50
Q

Renal changes in pregnancy

A

Rise in:
- GFR
- Kidney size
- Urinary collecting system size
- Glycosuria
- Proteinuria

51
Q

Amount GFR rises in pregnancy

A

50-70% increase

52
Q

Cause for increased glycosuria in pregnancy

A

Rise in GFR can overwhelm capacity for tubular re-absorption of glucose

53
Q

Why are UTIs and pyelonephritis more common in pregnancy

A

Dilated urinary collecting system (renal pelvis + calyces + ureters) leads to tendency of urine stasis

Also increased glycosuria

54
Q

Upper limit of normal proteinuria level in pregnancy

A

300 mg/24 hr collection

55
Q

Changes to plasma albumin concentration in pregnancy

A

Albumin concentration falls in early pregnancy and is then static up to term

56
Q

Mean urea concentration in pregnancy

A

3.3 mmol/L

57
Q

Mean creatinine concentration in pregnancy

A

51 micromol/L

58
Q

Hormones which change in pregnancy

A

Progesterone
Human chorionic gonadotrophin (hCG)
Human placental lactogen (hPL)
Aldosterone

59
Q

Progesterone changes in pregnancy

A

Concentration rises to a peak near term
Falls just before term - may contribute to initiation of labour

Progesterone responsible for many of the physiological changes of pregnancy

Vital for maintenance of pregnancy

60
Q

Alternate name for hPL (human placental lactogen)

A

Chorionic somatomammotrophin

61
Q

hPL features

A

Peptide hormone
Structure and function similar to growth hormone

62
Q

Consequence of raised hPL

A

Causes impaired glucose tolerance due to insulin resistance

63
Q

Aldosterone changes in pregnancy

A

Aldosterone secretion from adrenal cortex increases

Results in Na+ and water retention

64
Q

Metabolic changes in pregnancy

A

Rise in maternal basal metabolic rate

Also contributes to increased oxygen consumption

65
Q

hCG features

A

Peptide hormone

Produced by embryo and later by placenta

66
Q

Role of hCG in pregnancy

A

Maintain the corpus luteum and hence maintain progesterone production

Possible has a role in the altered immune system in pregnancy

Anaesthetic FRCA Primary - eLFH Obstetrics (6 decks)

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